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Aug I13, 194%. F. c. REEDER DIFFERENTIAL REGULATOR 2 Sheets-Sheet 1 Filed Dec. 10, 1936 M a. M

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Patented Aug. 13, 1940 UNITED STATES PATENT OF F ICE The' Fulton Sylphon Company,

Knoxville,

' Tenn., a corporation of Delaware Application December 10, 1936, Serial No. 115,220

12 Claim.

This invention pertains to air-conditioning, and more specifically to improved means for controlling the air-conditioning system. The invention is particularly designed for use in an airconditioning system in which air is drawn from the outside over heat exchanging means and circulated through the room or other compartment to be conditioned, and then is in part at least passed back through said system for reconditioning. The invention is capable of being adapted to any one of the three types of aircooling apparatus now in general use; to wit, the so-called ice-bunker systems, mechanical refrigerating systems and steam jet refrigerating systems, and therefore will 'be particularly described with reference to its use in air-cooling systems generally.

In the prior art an electrical thermostat has been most commonly used to stop and start the cooling unit, as the pump or the by-pass valve when an ice-bunker system is used, the motor or gas engine when the mechanical type is used, or the steam supply when the steam jet system is used, and ordinarily these thermostats are designed to maintain a given temperature in the compartment whereas it has been demonstrated that the most successful air-conditioning isobtained if the inside temperature is made to vary with the outside temperature.

Also these'devices of the prior art are open to a common objection in that they act intermittently and because of the resultant cycling or hunting a uniform temperature is not maintained for a given outdoor temperature, while the periodic starting and stopping of the cooling unit is productive of drafts, stratification of the air, etc. Likewise in the prior art systems the humidity of the conditioned air may vary greatly owing to the intermittent operation of the system, and particularly to the periods of rest during which dehumidiflcation may cease while the circulating air may pick up moisture from the coils and thereby increase the humidity in the compartment.

One object of the present invention is to provide an improved control which will give a relatively continuous and not intermittent action.

Another object of the invention is to provide an improved control which will maintain a predetermined relationship between the inside and outside air temperatures.

Another object is to provide an improved control which will at all times maintain the inside temperature in proper relation to the outside temperature by a continuous differential action.

Another object is to provide an improved control which will insure a substantially uniform in- 12:11:18.1 temperature for a given outdoor tempera- Another object is to provide an improved control whichwill gradually change the temperature of the conditioned air as required to maintain a desired indoor temperature.

Another object is to provide an improved control which will tend to prevent drafts and stratification, or rapid fluctuations in the temperature, of the conditioned air.

Another object is to provide an improved control which will gradually change the temperature of the conditioned air as the outside temperature changes so that the changes in the inside temperature are imperceptible.

Further objects of the invention will appear as this specification proceeds.

Typical embodiments of the invention are illustrated in the accompanying drawings but it is 20 trol means in a typical air-conditioning system in 30 which the control device is in part subjected to the temperature of the cooling medium; and

Fig. 3 illustrates an alternative installation in which the control device is in part subjected to the temperature of the recirculated air.

Referring first to Fig. 1, wherein the control is shown as applied to the actuation of a valve, as a valve in a water cooling system, the valve casing in is illustrated as having oppositely projecting nipples I l and I2 adapted to be connected in any suitable way to the system, as to sections of the cooling water return pipe. The valve may be of any suitable size and construction and is shown as having a pair of valve members l3 adapted to close ports it formed within the casing in any suitable way. Mounted on the valve casing Us a frame it, secured to the casing in any suitable way, and extending axially of said frame is the valve stem H which passes through apertures in frame l8 and the wall of the casing ii), a suitable packing gland it being provided to prevent leakage of liquid around said valve stem.

As shown, frame It has an intermediate transverse member i9 for a purpose hereinafter referred to, and it is shown as terminating in a flanged portion 20 to which is secured, in any suitable way as by screws 2 I, a cup-shaped outer wall 22-. Mounted concentrically within said cupshaped wall 22 in any suitable way is an expansible and collapsible corrugated tubular metallic wall 23 having one end suitably attached, as by soldering or brazing, to a rigid end wall 24 and its opposite end suitably attached, as by soldering or brazing,to an annular flanged member 25 which is suitably secured in the cup-shaped wall 22, as by soldering or brazing. Mounted concentrically within said expansible and collapsible wall 23 is a second expansible and collapsible corrugated tubular metallic wall 26 of smaller diameter than wall 23, said wall having one end suitably secured, as by soldering or brazing, to a rigid end wall 27 and its opposite end suitably secured, as by soldering or brazing, to an annular member 28 which in turn is suitably attached, as by soldering or brazing, to said annual member 25. Expansible and collapsible walls 23 and 26 are thus supported in telescopic relation with respect to each other and to the cup-shaped wall 22 and form two concentric hermetically sealed chambers, a chamber 29 between said cup-shaped wall 22 and said expansible and collapsible wall 23 and a chamber 30 between said expansible and collapsible walls 23' and 26.

Engaged with or attached to end wall 21, in any suitable way, is a valve stem extension 3| which is attached to the valve stem l! in any suitable way. as by a threaded connection 32 and lock nut 33. said valve stem extension 3| extending ax1aliy through an externally threaded tubular guide member 34 suitably mounted in the transverse member IQ of the frame |6 as by the threaded connection shown at 35. Threadedly mounted on the exterior of said tubular member 34 is an adjustable abutment 36 having a plurality of apertures 31 in its outer periphery so that, by engagement of a suitable tool with said apertures 31, said abutment element 36 may be rotated to advance or withdraw the same along the external threads of the member 34. Abuttlng said eiement 36, preferably with the interposition of a ball bearing 38 to reduce friction, is a cup-shaped spring socket member 39 having telescopic movement within a cylindrical guide member 40 fixedly mounted in any suitable way on the flange 20 of frame l6. Interposed between said socket member 39 and a second spring seat member 4| is a coil spring 42, spring seat member 4| being mounted on or attached to the valve stem extension 3| or the end wall 21 in any suitable way, the same being shown as attached to a tubular member 43 which at its opposite end abuts the end wall 21 or a centering member 44 for the valve stem extension 3| suitably mounted thereon. Therefore, by adjusting the element 36 the tension of the spring 42 may be adjusted to predetermine the tension with which the valve members |3 are held against their respective seats. Indicating means may be associated with said adjustment means, as shown.

Communicating in any suitable way with the chamber 29 is a nipple 45, here shown as fixed in an aperture formed in the cup-shaped wall 22, and suitably attached to said nipple 45 is a tube 46, which may be of any suitable size, construction, length and material and either flexible or rigid in character, leading to a bulb 41 of any suitable size, construction and material and designed to be mounted in any suitable way. Communicating with the chamber 30 is a tube 48, which may be attached to the annular member 28 in any suitable way, said tube 46 at its outer extremity communicating with a second nipple 49 mounted on the cup-shaped wall 22 or frame IS in any suitable way, said nipple 49 having suitably attached thereto a tube 50 which also may be of any suitable construction, length, size and material and either flexible or rigid in character, said tube at its outer extremity communicating with a second bulb 5| which may also be of any suitable size, construction and material and designed to be mounted in any suitable way.

The system composed of bulb 41, tube 46 and chamber 29 between the cup-shaped wall 22 and the expansible and collapsible wall 23 constitutes a thermostat of the bulb and motor-vessel type, and the same is charged with a volatile liquid of relatively low boiling temperature, for a purpose hereinafter explained, the tube 46 preferably extending into the bulb 4'! and forming a trap 52 therein so that the chamber 29 and tube 46 are normally maintained full of liquid, while the bulb 4'! is only partly filled with said volatile liquid and has a vapor space thereabove, with said vapor trapped in said bulb, so that changes of vapor pressure in said bulb will be transmitted through the liquid column in said tube 46 to the liquid in said chamber 29 to thereby exert varying pressures on the movable end wall 24.

The system composed of bulb 5|, tube 50 and annular chamber 30 between the expansible and collapsible walls 23 and 26 constitutes a second thermostat of the bulb and motor-vessel type, and said thermostat is charged with a suitable volatile liquid of a higher boiling temperature than that used in thermostat 41, 46, 29. Here also tube 56 is preferably extended into the bulb 5| and forms a trap 53, and the chamber 30 and tube 46 are preferably maintained full of liquid while bulb 5| is partly filled with said liquid but has a vapor space thereabove with the vapor trapped therein, so that fluctuations of vapor pressure in said bulb 5| are transmitted through the liquid column in tube 50 to the liquid in said chamber 30.

End wall 24 is not attached to end wall 21 but the two are always maintained in engagement by reason of the fact that the volatile liquids of the two thermostats are so chosen that the pressure in the chamber 29 is always greater under normal operating conditions than the pressure in chamber 30, while the coil spring 42 reacts upon end wall 2'! so as to maintain it in engagement with the end wall 24 during opening and closing movements of the valve.

Referring next to Fig. 2, a suitable installation of the control as heretofore described is illustrated somewhat diagrammatically. As here shown an air duct 60 formed in any suitable way in the wall of the room or other compartment has disposed therein a suitable heat exchanging unit 6| connected by feed pipe 62 and return pipe 63 with any suitable provision for cooling the circulating liquid, indicated at 64. As here shown, the valve I6 is disposed in the return pipe 63 and the bulb 41 is suitably mounted in a section of said return pipe, i. e., in the pipe 65 between the heat exchanger 6| and valve casing ID, as by a T 66. Bulb 5| is mounted in any suitable way, as by a bracket 6'! and a clip 68, adjacent the opening 69 through-which air enters the duct 60 from the outside and which may be provided with suitable shutters, a grill or other means. The duct is also provided with an opening 10 through which air is returned to the duct 60 from the compartment, said opening also being provided with suitable shutters, a grill or other means. Mounted in any suitable way in the .duct above the heat exchanger 6| is a fan 1| of any suitable size and construction for drawing the air through the heat exchanger ti and delivering it to the compartment to be conditioned. The openings 69 and 10 are suitably designed or adjusted so as to predetermine the relative quantity of air taken in from the outside to the quantity of air recirculated from the compartment being conditioned,

the ratio of fresh air drawn through the opening 69 to the recirculating air drawn through the opening 10 ordinarily being between 25% and of theentire air passed through theduct 60.

Fig. 3 illustrates another installation of the control in an air-conditioning system. In this embodiment the temperature responsive bulb 41 is placed in or adjacent to the return air opening 10 rather than in the return pipe of the cooling water system. Otherwise the system may be the same as that above described in conjunction with Figs. 1 and 2. Othersuitable positions for the bulb 41 may be chosen; for example, the bulb 41 may be disposed adjacent to or in contact with the evaporator so as to be responsive to the temperature of the refrigerant therein. While the control has been illustrated as connected to a valve for controlling the flow of cooling medium through the heat exchanger, this is not essential, as before pointed out, as the control may be applied to other means for predetermining the action of the cooling unit, either to vary the quan- I tity of cooling medium in circulation or to vary the operation of the means which effects the circulation of the cooling medium, as the control of a rheostat for the electric motor or the governor of an engine for driving the compressor of a. mechanical refrigerating system, for example.

The control as applied to a valve in a water cooling system functions in the following manner:-Temperature responsive bulb 41 is located in the return water pipe of the air-conditioning system and the fluid contained therein is responsive to the heat of said return water and generates a. pressure which is transmitted to the expansible and collapsible chamber 28 and applied to end wall 24 thereof. Temperature responsive bulb 5! is positioned in the air intake opening and the fluid contained therein is responsive to the heat of the intake air and generates a pressure which is transmitted to the expansible and contractible chamber 30 where it is also applied to the end wall 24, the end wall 21 being normally held in contact with the end wall 24 due to the action of spring 42. Thereby variations in outside air and cooling water temperatures are differentially applied to the end wall 24 and thence to the end wall 21 and valve stem, and the valve is opened or closed as the relationship of said differential pressure varies with respect to the tension of the spring 42, which in turn may be adjusted to vary the operation of the control.

For example, if the outdoor air remains at a constant temperature, the circulated air picks up heat from the persons in the room, and this heat chamber 29 to expand, thus increasing the valve opening and causing more cooling medium to circulate. If the outdoor temperature increases there is a vaporization of the fluid in bulb 5| which acts on end wall 24 to decrease the net pressure thereon and therefore the expansible and pressure of the fluid contained in the bulb 5| with a resultant increase in the net pressure on end wall 24 whereby the valve is opened to increase the cooling effect and correspondingly decrease the temperature in the room.

As may be readily seen, the valve is always subject to the difierential action of the two expansible and contractible chambers 28 and 30,

and as.the temperature of the outside air varies the valve is gradually moved to maintain a predetermined relationship between indoor and outdoor temperatures. Since chamber 29 is responsive to changes in indoor temperature either directly as in Fig. 3 or indirectly through the temperature of the cooling water as in Fig. 2,

while chamber 30 is responsive to outdoor temperature, the result of this differential action is a steady, continuousand gradual control of the conditioned air, without sudden shocking changes, stratiflcation of the air, drafts, etc.

The fluid charges in the two thermostats may be varied according to the relationship desired between outside temperature and inside temperature, it being understood that the fluid in thermostat 41, 46, 29 is always of the lower boiling temperature so that the pressure in chamber 29 is always higher than in chamber 30. Like wise, spring 42 is adjustable by element 36 and by varying its tension the initial pressure differential between expansible and contractible cham= bers 29 and 30 required to open the valve may be precisely determined.

As stated before, the charge in bulb 41 has a lower boiling point than the charge in bulb 5|, and these boiling points may be so selected that the vapor pressure in chamber 29 at all times is so related to .the vapor pressure in chamber 30 that a definite relationship between the two is maintained. For example, the regulator may be so designed that with a temperature at bulb 5| of 80 F. the valve will operate to maintain a temperature at bulb 41 of 54 F., and when the temperature at bulb 5| is increased to 100 F. the pressure in the chamber 30 between the two bellows is so increased, which is equivalent in effect to a decrease in the pressure in chamber 29, that an increase in the pressure in the chamber 29 corresponding to an increase in temperature of 5 F. at the bulb 41 is required to bring the valve back to its former position, it being understood that these increased temperatures at bulb 41 are assumed to be those required for maintenance of the desired room temperatures.

' Thus, a typical example of the operation of the regulator would then be as follows. If the regulator is designed so that when the temperature of bulb 5| is at 80 F. and the temperature at bulb 41 is 54 F., corresponding to an indoor temperature of F., an increase in the temperature at bulb M from to .F. would cause the operating temperature at bulb 41 to increase to 595 F., thereby to increase the indoor temperature from "75 to 80 F. By varying the thermostatlc charges in the two thermostats, this 7 differential may be varied over wide ranges. In other words, for the same initial relationship as given above, 1. e., with bulb 5| at F. the bulb 41 is at 54 F., the thermostatic charges can be so selected that a change in the temperature at bulb 5| from 80 F. to F. will increase the temperature at bulb 41 to correspond with indoor temperatures of 77, 79, 802 833, etc., as preferred.

When the alternative embodiment of the invention illustrated in Fig. 3 is employed, bulb I1 is placed in the recirculating air opening and thus the fluid in the bulb 41 is responsive directly to the temperature changes of the air in the conditioned room. But with this alternative embodiment the same difierential action between the expansible and contractible chambers 29 and 30 is maintained, and the system functions in precisely the same manner as in the embodiment first described.

The present invention also attains a practically straight line control of the indoor temperature. Moreover, the control is purely automatic and the human factor need not enter. Furthermore, the inside temperature is always correct with reference to the outside temperature, and temperature changes within the room are so gradual as not to be noticeable to the occupants.

The present control may be adapted to many different types of conditioning systems. The illustrated embodiment operates as a regulator for the flow of water in a water-cooled system, but it may likewise be applied to a system using a motor driven compressor, in which case the thermostatic system could be applied to a suitable governor to control the speed of the engine or to a suitable rheostat to control the speed of the electric motor. Likewise the control may be used in steam jet refrigeration.

By preference the air-conditioning system is so designed that the cooling unit is maintained constantly in operation. By suitably designing the element to be controlled said element may be maintained in such a position that the system varies in capacity but is continuously in operation for abstraction of so much heat from the circulating air as is necessary to maintain trk indoor temperature substantially uniform as long as the outdoor temperature remains uniform or to gradually and progressively change the indoor temperature to maintain the predetermined relationship with the outdoor temperature it the outdoor temperature varies. Thereby the present invention avoids the fluctuations of temperature, in hunting or cycling, incident to a system 'that is periodically started and stopped, while any change in indoor temperature necessitated by a change in outdoor temperature is eflected so gradually as to be imperceptible to occupants of the room or other compartment, and at the same time the continuous operation of the system without sudden fluctuations of temperature arising from the starting and stopping of the same is also effective in avoiding drafts and stratiflcation of the air, a more uniform temperature being maintained throughout the room or other compartment.

While the invention has been particularly described in connection with its use as a control for a cooling system, it is to be understood that the invention is also applicable to a control for a heating system, in which event the heat ex changer imparts heat to the air rather than abstracts heat from the air, and the differential control of the compound thermostat as herein described is applied to the regulation of the heating medium so as to maintain the desired differential in heat delivery, which can compensate for heat loss through the walls at different outdoor temperatures, it being understood that the charges of the respective thermostats will be so selected as tomaintain the desired predetermined relationship between indoor and outdoor temperatures. Therefore the term "air-conditioning as herein used is intended to embrace heat- 'ing as well as cooling of the air.

While the embodiments of the invention illustrated on the drawings have been described with considerable particularity, it is to be expressly understood that the invention is not to be restricted thereto, as the same is capable of receiving a variety of expressions, some of which will now readily suggest themselves to those skilled in the art, while changes may be made in the details of construction, arrangement and proportion of parts and other forms of differentially operating thermostats may be employed, etc., without departing from the broader aspects of this invention. Reference is therefore to be had .to the appended claims for a definition of said invention.

What is claimed is:

1. In a control for an air conditioning system, in combination with controlling means for said system, means for operating said controlling means including two telescopically arranged expansible and contractible fluid-tight chambers each having a movable end wall, resilient means for urging the end wall of the inner chamber toward the end wall of the outer chamber, a bulb in communication with each of said chambers,

each bulb and its communicating chamber being charged with a volatile liquid and the liquid charge of the outer of said chambers and its bulb being of lower boiling point whereby the higher fluid pressure in said outer chamber normally urges the end wall of said outer chamber into contact with the end wall of said inner chamber, andmeans operatively connecting said movable and walls to saidcontrolling means.

2. In a control for an air conditioning system, in combination with controlling means for said system, means for operating said controlling means including two telescopically arranged expansible and contractible fluid-tight chambers each having a movable end wall, a bulb in coinmunication with each of said chambers, each bulb and its communicating chamber being charged with a volatile liquid and the liquid charge in the outer of said chambers and its bulb being of lower boiling point whereby the fluid pressure in said outer chamber is normally higher than the fluid pressure in said inner chamber, means operatively connecting said movable end wall to said controlling means, and resilient means associated with said last namedmeans and adjustable to predetermine the operative difference in fluid pressure existing in said chambers, said end walls being urged into contact by the action of said resilient means and the pres: sure in said outer chamber.

3. In a control for an air conditioning system, in combination with controlling means for said system, a rigid cup-shaped exterior wall, two telescopically arranged expansiblc and collapsible walls telescopically arranged within said rigid wall and each having a movable end wall secured thereto, said walls providing a pair of telescopically arranged expansible and collapsible chambers, a bulb in communication with each of said chambers, each of said bulbs and its communicating chamber being charged with a volatile liquid and the liquid charge in the outer of said chambers and its bulb being of a lower boiling point, resilient means cooperating with the higher fluid pressure in said outer chamber to maintain said end walls normally in contact and a-single member operated at all times by the conjoint action of both of said movable end walls for determining the position of said controlling means.

4. In a control for an air conditioning system, in combination with controlling means for said system, a rigid cup-shaped exterior wall, two telescopically arranged expansible and collapsible walls telescopically arranged within said rigid wall and each having a movable end wall secured thereto, said walls providing a pair of telescopically arranged expansible and collapsible chambers, a bulb in communication with each of said chambers, each of said bulbs and its communicating chamber being charged with a volatile liquid and the liquid charge in the inner of said chambers and its bulb being of a higher boiling point, a single member operated by the conjoint action of said movable end walls for determining the position of said controlling means, and resilient means associated with said last named member and acting in opposition to the higher fluid pressure in said outer chamber to hold said movable end walls in contact and adjustable to predetermine the operative difierence in fluid pressure existing in said chambers.

5. In a control for an air conditioning system, in combination with controlling means for said system, a pair of telescopically arranged expansible and contractible fluid-tight chambers each provided with a movable end wall, a bulb in communication with each of said chambers, each of said bulbs and its communicating chamber being charged with a volatile liquid and thevola-tile liquid in one of said bulbs and its communicating chamber having a higher boiling point than that in the other bulb and chamber, resilient means acting in opposition to the higher fluid pressure of said fluid of lower boiling point to hold said movable end walls in contact and means operacontrolling means;

6. In a control for an air conditioning system, in combination with controlling means for said system, a pair of telescopically arranged expansible and contractible fluid-tight chambers each provided with a movable end wall, a bulb in communication with each of said chambers, each of said bulbs and its communicating chamber being charged with a volatile liquid and the volatile liquid in one of said bulbs and its communicating chamber having a higher boiling point than that in the other bulb and chamber, means operatively connecting said movable end walls to said controlling means, and resilient means associated with said last named means and adjustable to predetermine the diflerence in fluid pressure existing in said chambers, said resilient means acting in opposition to the higher fluid pressureto hold said movable end walls in contact.

7. In a control for an air conditioning system, in combination with controlling means for said system, a pair of concentrically arranged expansible and contractible fluid-tight chambers each provided with a movable end wall, a bulb in communication with each of said chambers, each of said bulbs and its communicating chamber being charged with a volatile liquid, the volatile liquid in one of said bulbsand its communicating chamber having a higher boiling point than that in the other bulb and chamber, means subjecting the bulb containing the volatile liquid of lower boiling oint to a temperature which varies with variations of temperature in the space to be air conditioned, means subjecting the bulb containing the volatile liquid of higher boiling point to a temperature which varies with the outdoor temperature, resilient means cooperating with the higher fluid pressure in the chamber contain; ing the fluid of lower boiling point for holding said movable end walls in contact and the fluid pressure in said chamber containing fluid of higher boiling point varying the pressure at which the pressure, in said first named chamber actuates said contacting movable end walls, and means operatively connecting said movable en walls with said controlling means.

8. In a control for an air conditioning system,

in combination with controlling means for said system, a pair of concentrically arranged expansible and contractible fluid-tight chambers each provided with a movable end wall, a bulb in communication with each of said chambers, each of said bulbs and its communicating chamber being charged with a volatile liquid, the volatile liquid in one of said bulbs and its communicating chamber having a higher boiling point than that in the other bulb and chamber, means subjecting the bulb containing the volatile liquid of lower boiling point to a temperature'which varies with variations of temperature in the space to .be air conditioned, means subjecting the bulb containing the volatile liquid of higher boiling point to a temperature which varies with the outdoor temperature, resilient means cooperating with the higher fluid pressure in the chamber containing the fluid of lower boiling point for holding said movable end walls in contact and the fluid pressure in said chamber containing fluid of higher boiling point varying the pressure at which the pressure in said first named chamber actuates said contacting movable end walls, means operatively connecting said movable end walls with said controlling means, and means associated with said resilient means for adjusting the effective difference in pressure in said two chambers.

9. In a control for an air conditioning system, the combination of controlling means for said system, a pair of telescopically arranged expansible and contractible' fluid-tight chambers each provided with a movable end wall, a bulb in communication with each of said chambers, each of said bulbs and its communicating chamber be- I ing charged with a volatile liquid and the liquid in the inner of said chambers'and its associated bulb having a higher boiling point than that in the other bulb and chamber, means mounting the bulb associated with the outer of said chambers where it is responsive to a temperature which varies with the temperature of the space to be air conditioned, means mounting the bulb associated with the inner of said chambers where it is responsive to a temperature that varies with the outdoor temperature, resilient means cooperating with said movable end walls and coacting with the difierence in fluid pressure in said chambers to hold said movable end walls in contact, and means operatively connecting said movable end walls with said controlling means.

10. In a control for an air conditioning system,

the combination of controlling means (or said system, a pair of telescopically arranged expansible and contractible fluid-tight chambers each provided with a movable and wall, a bulb in communication with each of said chambers, each of said bulbs and its communicating charm her being charged with a volatile liquid and the liquid in the inner of said chambers and its associated bulb having a higher boiling point than that in the other bulb and chamber, means mounting the bulb associated with the outer or said chambers where it is responsive to a temperature which varies with the temperature 01 the space to be air conditioned, means mounting the bulb associated with the inner of said chambers where it is responsive to a temperature that varies with the outdoor temperature, means oneratively connecting said movable end walls with said controlling means, and resilient means associated with said connecting means and acting in opposition to the resultant of the pressure existing in said chambers to hold said movable end walls in contact.

11. In a control for an air conditioning system, in combination with controlling means for said system, a rigid cup-shaped wall, a pair of telescopically arranged expan'sible and collapsible walls telescopically mounted within said rigid wall and each provided with a movable end wall,

- said walls providing a pair of expansible and collapsible chambers, a bulb in communication with each of said chambers, each of said bulbs and its communicating chamber being charged with a volatile liquid and the liquid in the outer of said chambers and its associated bulb having a lower boiling point than that in-the other bulb and chamber, resilient means acting in opposition to the higher fluid pressure in said outer chamber to urge said end walls into contact, means mounting the bulb associated with the outer chamber where it responds to a temperature which varies with the temperature in the space to be air conditioned, means mounting the other of said bulbs where it is responsive to a temperature which varies with the outdoor temperature, and a single member adapted to be operated by the con- Joint action of said movable end walls for determining the position of said controlling means.

12. In a control for an air conditioning system, in combination with controlling means for said system, a rigid cup-shaped wall, a pair of telescopically arranged expansi'ble andcollapsible .walls telescopically mounted within said rigid wall and each provided with a movable end wall, said walls providing apair of expansible and collapsible chambers, a bulb in communication with each of said chambers, each of said bulbs and its communicating chamber being charged with a volatile liquid, and the liquid in the outer of said chambers and its associated bulb having a lower boiling point than that in the other bulb and chamber, resilient means acting in opposition to the higher fluid pressure in said outer chamber to urge said end walls into contact, means mounting the bulb associated with the outer chamber where it responds to a temperature which varies with the temperature in the space to be air conditioned, means mounting the other of said bulbs where it is responsive to a temperature which varies with the outdoor temperature, a single member adapted to be operated by the conjoint action of said movable end walls for determining the position of said controlling means, and means associated with said connecting member and operable to adjust said resilient means to predetermine the efiective difierence in fluid pressure which shall exist in said chambers. Y FRANK C. REEDER. 

